As the performance, density and cost considerations of electronic apparatus become more stringent the structure is evolving into a tightly packed arrangement of interconnected device bearing boards with a large quantity of very closely positioned contacts. Those contacts cannot be permitted to introduce impedance into the interconnecting system and the conductors, in turn, in the interconnecting system cannot be permitted to introduce an impedance limitation on the transmission of the signals. Further, the large numbers of contacts must be such that they can be fabricated without introducing non-uniformity and reliability problems as is the situation where meticulous care is not taken to prevent metal oxides, grease, corrosion, insulating material particles and other debris from getting between the mating surfaces.
One contacting technique receiving attention in the art involves a pad on one member contacting a pad on another member with the pads being held in position in service by a structure that supplies approximately constant pressure. The technique is known in the art by the terminology "pad on pad". In high density electronic apparatus there is very little space to accommodate structure associated with contacts. The pad on pad type contact occupies a small area.
In the pad on pad type of contacting, reliability, uniformity and impedance minimization is greatly improved where a wiping operation of one pad on the other can be supplied when the pads are brought together. Heretofore in the art however, the providing of constant pressure in service and the providing of a wiping operation introduce considerable added structure in an interconnecting system. In many applications there just isn't room for any added structure.
One type of electronic apparatus wiring employs a dielectric supporting member with flexible conductors on or embedded in it. It is known in the art as "flex tape". In the "flex tape" the dielectric supported wiring conductors are available with precision electric transmission line properties and with ground planes where desired. The flexibility simplifies large array assembly. The wiring benefits of "flex tape" wiring in electronic apparatus are somewhat offset by the difficulty and added structure needed for connection to "flex tape" and between "flex tapes".
One example of that added structure in applying constant pressure in service is shown in U.S. Pat. No. 4,948,374 wherein pads on a "flex tape" are retained in contact with pads on a printed circuit board in a housing that has a bow spring and a deformable pad urging the pads together.
Pad on pad connections to "flex tape" conductors where there is also wiping of the pads as they are assembled has heretofore in the art been confined to structures where the "flex tape" conductors are supported by a rigid supporting member.
As an example, in U.S. Pat. No. 4,740,867 a connecting structure is shown where the "flex tape" is clamped in a slotted housing and a rigid connector member enters the slot, wipes and makes contact with the flex tape conductors.
There is a need in the art for the ability to make reliable, uniform, and low cost, pad on pad connections, to all types of substrates, both rigid and flexible, without complex associated structure.